In China, about 75% of energy source depends on coal, and therefore coal dust and SO2 emission have been a big environmental problem. According to the White Paper on Environment in China, emission of SO2 chiefly supplied by combustion of coal, amounted to approximately 18 million tons in 1993.
In urban area of southern parts of China such as Chongqing, Guiyang, and Changsha, air pollution and acid rain arising from the coal combustion have Changsha, air pollution and acid rain arising from the coal combustion have caused serious damages to forest and crop. However, acid rain has spread in another cities, recently. The Chongqing City, located in Sichuan Province is highly industrialized region with a population of about 1. 5 millions. Especially, in the Center District, population density and industrial activities are very large. In the city, coal with high sulfur content is mainly used for energy production, and therefore heavy air pollution and acid rain have been observed around the center of the city. Decline of the masson pine forest at Nanshan Mountain and effects of air pollution on human health have been reported (Feng et al. , 1993).
As a part of Grant-in-Aid for Creative Fundamental Research, sponsored by the Ministry of Education, Science and Culture of Japan, "Studies of Global Environmental Change with Special Reference to Asia and Pacific Regions" were started in 1990. As one of this study, the Japan and China co-operative studies on impacts and control strategies of acid deposition on terrestrial ecosystems have been carried out at Chongqing area.
We held the symposium two times, in 1991 at Fuchu, and in 1992 at Beijing, and preliminary results were reported at these symposiums (Ogura, 1991; Feng and Ogura, 1993), and the final symposium was held in 1994 at Beijing (Feng et al. , 1995),
In the present paper, the final results of the present co-operative study are summarized, in connection with the following three parts :
Co-operative studies were carried out at Nanshan Mountain area (urban site: about 10 km from the City Center) and Jinyun Mountain area (unpolluted suburb site: about 60 km from the City Center) (Fig. 1).
Zhenwu Mountain in Nanshan Mountain area has been covered with masson pine, however most of the trees were dead during 1982 to 1983 by complex combinations of acid rain, acid fog, air pollution, pests and diseases.
Samples of air pollutants and rain waters were collected during June 1991-May 1992 at Zhenwu Mountain (inside station of the forest) and at the rooftop of Forest Diseases & Pest Prevention Station (outside station of the forest), in Nanshan Mountain area (Fig. 2).
Gaseous and aerosol samples were collected at two sampling sites by using a filter pack holding two filters. The air was drawn through the filter pack by a pump at a flow rate 0. 4 1/min.
Particulate or aerosol species collected on the filters were extracted by deionized water. Impregnated filters with mixture of sodium carbonate-glycerin for acidic gases were extracted by deionzed water with a few drops of 30% hydrogen peroxide. All extract solutions were analyzed by ion chromatography.
Monthly changes of air temperature at outside and inside of the forest are shown in Fig. 3. Maximum, about 29¡C was observed in July and minimum, about 8¡C, was observed in January.
Monthly changes in SO2 and aerosol sulfate (SO4) are shown in Fig. 4 at each site. Concentration of SO2 was very and its annual mean concentration amounted to 220 mg/m3 at outside of the forest, which was 7. 7 times higher than that in Japan . However its concentration was approximately 30% smaller at inside of the forest (mean 155 mg/m3). Higher SO2 concentrations were observed during November to January when air temperature was lower. Maximum, 360 mg/3 was observed in January, which exceeds the Chinese national third standard value of 250 mg/m3. These seasonal variation is considered to be resulted from weather conditions and partly from seasonal coal combustion pattern.
A 10 1 sampler was set on the rooftop of the Forest Diseases and Pest Prevention Station, and a polyethylene funnel of 148 am diameter was installed. Throughfall was collected under canopies of the masson pine forest in Zhenwu Mountain, and stemflow was collected from stems of the trees by using polyethylene tube to lead into the samplers. These rain water samples were gathered each 10 day, and ion compositions were analyzed by ion chromatography for anions, and atomic absorption spectrometry for cations, and colorimetry for NH4.
Ion concentrations in rain water, especially stem flow, were very high compared with data in Japan (Table 1).
Table 1 Chemical Composition of Rainfall at Zhenwu Mt. (June 1991-May 1992) (Zhang et al., 1993)
| Rainfall | pH | CI- | SO42- | NO3- | Na+ | K+ | Ca2+ | Mg2+ | NH4+ | |
| mm | µeq/1 | |||||||||
| Precipitation | 1240 | 4.6 | 27.6 | 469 | 45 | 23.9 | 82.6 | 418 | 40.3 | 106 |
| Throughfall | 867 | 3.8 | 64.6 | 1008 | 69.8 | 34.8 | 171 | 629 | 88.8 | 258 |
| Stemflow | 0.79 | 2.9 | 116 | 4083 | 192 | 94.8 | 272 | 1505 | 211 | 1073 |
Concentrations of sulfate and calcium ions are especially high, compared with other ion species. Mean annual SO4 and calcium concentrations were 469, 418 meq/1, respectively.
Monthly changes of sulfate ion are shown in Fig. 5. Higher concentrations were observed in December to January and lower during summer season. These tendencies were in agreement with gaseous SO2 changes. However, monthly variations of sulfate deposition are not clear, compared with those of concentration.
Annual deposition of sulfur by throughfall and stemflow was 8750 equivalent/ha, which was considerably higher compared with the results in other forests of relatively heavy pollution.
From the continuous monitoring of air pollutants and rainwater, annual atmospheric deposition of sulfur on the urban coniferous forest, at Zhenwu Mountain was calculated (Fig. 6). This amounted to 187 kgS/ha. yr. , of which about 50% was wet SO4 in rain, 25% was dry deposition on the forest crown, and 25% was dry deposition on the forest floor.
Samples of pond waters were collected during 1991-1992 at Nanshan Mountain and Jinyun Mountain areas, and water qualities and biological parameters were determined.
In acidified small ponds at urban and suburb areas, concentrations of aluminum and SO4 were high (Table 2).
Table 2 Physical and Chemical Parameters of the Studied Pond Waters (Xia et al., 1995)
| Types of Waters | Acid | Less Acid | Normal | |||
| A1 | A2 | L3 | L4 | N5 | N6 | |
| pH | 4.24 | 4.69 | 5.08 | 5.55 | 7 | 8.45 |
| Trans. (m) | 5.8 | 5.1 | 0.4 | 0.3 | 1 | 0.5 |
| Sulfate (mg/1) | 20 | 20.5 | 10.3 | 19.2 | 15.8 | 52 |
| Total P (mg/1) | 0.03 | 0.03 | 0.08 | 0.06 | 0.08 | 0.09 |
| Total Al (mg/1) | 2.32 | 1.89 | 0.31 | 0.29 | 0.24 | 0.25 |
Numbers of species, and standing crop of phytoplankton were considerably smaller in acidic ponds compared with those in normal ponds (Table 3).
Standing crops of zoobenthos, oligochaete were low, however that of chironomus was high in acidified ponds. Therefore, it is considered that water acidification has a great influence on aquatic ecosystem and resulted in significant changes of its function.
Table 3 Total Species Numbers of Algae Recorded in the Studied Pond Waters (Xia et al., 1995)
| Species Numbers | |||
| Acid | Less Acid | Normal | |
| Chlorophyceae | 13[52] | 23[58] | 23[54] |
| Cyanophyceae | 3[12] | 6[15] | 7[16] |
| Bacillariophyceae | 5[20] | 4[10] | 6[14] |
| Others | 4[16] | 7[18] | 7[16] |
| Total | 25[100] | 40[100] | 43[100] |
Others: Euglena, Cryptophyceae, Pyranophyceae and chrysophceae Parenthesized figures sre percent to the total.
Investigations on forest ecosystems were carried out during 1992-1993 in coniferous (masson pine) and broad-leaved (camphor tree) forests.
Biomass of the forest of masson pine and camphor tree in Nanshan Mountain are shown in Table 4. Especially biomass of the masson pine was small. From these results, it was found that net productivity of the forest, especially masson pine forest, was very low compared other normal forests.
Table 4 Biomass of Forest of Masson pine and Camphor Trees Grown in the Nanshan Area (Totsuka et al.,1995)
| Item | Forest of masson pine (Zhen wu shan) | Forest of camphortree (Lao jun dong) |
| Diameter of breast height (cm) | 13.3 | 22.5 |
| Tree height (m) | 9.1 | 16.4 |
| Total dry weight (kg/m2) | 2.1 | 13.6 |
| Shoot dry weight (kg/m2) | 1.9 | 6.5 |
| Leaf Dry weight (kg/m2) | 0.08 | 0.43 |
| Leaf area index | --- | 1.1 |
| Net oroduction of forest (kg/m2/year) | 0.07 | 0.52 |
| Standing crop of undergrowth (kg dw/m2) | 0.19 | o.33 |
Sulfur and fluorine contents in leaves of the masson pine trees at the urban forest in Zhenwu Mountain were 2. 3 times higher than those at the unpolluted suburb forest in Jinyun Mountain. Therefore, at the urban forest, fluorine may have some influences on forest decline, in addition to SO2.
According to the laboratory experiments, significant effects were observed by exposure of 50 ppb SO2 and soil acidification on the dry weight growth of the seedling of masson pine tree (Fig. 7).
Studies on soil chemistry were carried out during 1993-1994. Soil solution was extracted by an apparatus equipped with a porous ceramic cup applying a suction of 80 kPa.
The pH of soil ranged from 4. 3 to 5. 0, and pH was not different between samples under masson pine and camphor trees. However, pH of soil solution under the masson pine trees was significantly lower than that under the camphor trees (Table 5).
Table 5 pH of Soil and Soil Solution (Okazaki et al., 1995)
| Soil | Soil Solution | |
| Masson pine tree (Zhenwu Mt.) | 4.4 - 5.0 | 4.3 - 4.6 |
| Camphor tree (Laojundong) | 4.3 - 5.0 | 4.5 - 5.0 |
June 1993 - May 1994
Monthly variations of sulfate and nitrate concentrations in soil solution are shown in Fig. 8. Sulfate concentration under the masson pine tree was three times higher than that under the camphor trees. Nitrate concentration under the masson pine trees was over ten times higher than that under the camphor trees. From these results, it is considered that broad-leaved forest may reduce acidification of yellow soil to some extent.
Coal samples used in Chongqing City were obtained 4 coal-mines. Sulfur contents of these coals amounted to 4 to 5% (Table 6).
Table 6 Analytical Results of Coal Samples (Sugawara et al., 1995)
| Sample | C [wt%,daf] | S [wt%,dry] | Ash [wt%,dry] | Pyritic Organic [wt% of total sulfur] | |
| Nan Tong | 89.5 | 4.1 | 17.8 | 34 | 66 |
| Zhong Liang Shan | 90.1 | 4.3 | 18 | 68 | 32 |
| Fu Rong | 90.1 | 5.2 | 22.6 | 77 | 23 |
| Yanzhou (Beishu) | 89.2 | 2.9 | 9.1 | 38 | 61 |
Annual emission of SO2 amouns to 0. 41 million tons (0. 41 Tera g) in Chongqing City, this is approximately 5% of the total Chinese emissions (Zhao et al. ,1994). Therefore, countermeasure of SO2 emission is very important problem in Chongqing City. Contribution of different coal combustion facilities to the total SO2 emission in Chongqing City was estimated as shown in Fig. 9. Domestic use amounted to 38% of the total emission, medium & small scale factories and power plant & large scale factories were 33% and 29%, respectively.
Predesulfurization of high sulfur coals by rapid-pyrolysis combined with density separation was examined. This shows a correlation between extent of organic sulfur removal and average specific gravity. In general, lower the specific garvity, higher the extent of organic sulfur removal. In case of the Fu Rong coal, most of organic sulfur was removed rapidly.
The effect of briquet combustion, that is addition of calcium carbonate to coal, on reduction of SO2 emission was examined. In general, the ratio of Ca to S (Ca/S) becomes higher, desulfurization efficiency increased and amounted to approximately 60 to 70%.
The cost of coal briquet, including facility cost, utility cost and desulfurization agent cost, was estimated and compared with the cost of the fluidized bed or semi-dry processes. The desulfurization cost using coal briquetting reduced to less than half compared with that of semi-dry or fluidized bed desulfurization process (Fig. 10).
The most important counterplans for the present are reduction of SO2 emission from stationary sources.
In case of the power station and large-scale boiler, the following counterplans are useful, that is washing of coal at mine sites, desulfurization in fluid-bed combustion and semi-dry flue-gas desulfurization. In case of the middle and small scale boiler, and private use for cooking, the followings are useful, that is briquetting with lime stone, and use of coal char prepared by washing and rapid-pyrolysis at mine sites.
In order to prevent decline of forests, reduction of SO2 and fluorine emission is important, moreover, neutralization of soil by sprinkle of lime under the forest floor is considered to be also useful. In addition, change of coniferous trees into broad-leaved trees, which is comparatively song to acidification of soil, may be also an effectual method.
At the Chongqing power station, countermeasures for SO2 and dust are not enough. However, the new power station equipped with desulfurization equipment and electric dust collector was constructed at the suburb of Chongqing City in 1991. At Nanshan Mountain area, mixed planting of coniferous and broad-leaved trees has been tried and recovery of fertility of soil is expected.
Finally, the following future research problems are considered, in order to recover the clean air and comfortable environment :
Feng,Z. W. and Ogura, N. (Eds. )(1993): Proc. of China-Japan Joint Symp. on the Impacts and Control Strategies of Acid Deposition on Terrestrial Ecosystems. Nov. 1992, Beijing, China Sciences & Technology Press, 227 p.
Feng,Z. W. , Chen,C. Y. and Zhang,J. (1993): Research progress on the effects of acid deposition of forest in Southwestern China. In, Proc. of China-Japan Joint Symp. on the Impacts and Control Strategies of Acid Deposition on Terrestrial Ecosystems. 62-77, China Sciences & Technology Press, 227 p.
Feng,Z. W. , Liu, C. M. , Ogura,N. and Matsumoto, S. (Eds. )(1995) : Proc. of China-Japan Joint Symp. : Impacts of Salinization and Acidification on Terrestrial Ecosystems and Their Rehabilitation in East Asia. Nov. 1994, Beijing, China, 231 p.
Ogura, N. (Eds. )(1992) : Proc. of Internat. Symp. on Impacts of Salinization and Acidification on Terrestrial Ecosystem and Its Rehabilitation. Sep. 1991, Fuchu, Tokyo, 243 p.
Zhao, D. , Hans, M. S. , Zhao, D. and Zhang D. (1994) : Pattern and cause of acidic deposition in the Chongqing region, Sichuan Province, China. Water, Air and Soil Pollution 77, 27-48.